He could have been a salesman since he is one at the start of the game, but he also manages to give the cafe at the end of year 1 a complete makeover, to the Calavera Cafe (plus Casino), so I think he has decent managing capabilities as well. Maybe he already had his own cafe/restaurant when he was alive..

We may have years, we may have hours, but sooner or later, we push up flowers.

I always imagined Manny as a sucessful door-to-door vacuum cleaner salesman and finally after annoying thousands of customers finally one person buys a vacuum and he gets hit by a car as he steps out into the street with the money in his hand.

Calavera seems like just the right person to sell vacuum cleaners.
It takes a lot of convincing to make someone buy a vacuum cleaner at the door. That'd also explain how he got the ship from the captain in year 3. A LOT of convincing.
But I think he sold bad suits. "Suits" him better.

He was black, thats why he had to do the community service in the afterworld.

...Woah.

Manny being a salesman when he was alive seems plausible. It makes sense to think that when he got to the Land of the Dead, the "powers that be" might of stuck him in a job that he already had some previous experience in.